From Hard Drop - Tetris Wiki

Triple Double Attack, sometimes referred to as Triple-Double, C-Spin, or just plainly TD, is a T-Spin combo that consists of a T-Spin Triple followed by a T-Spin Double. A player performs a T-Spin Triple that leads into a T-Spin Double.

When referring to the term "TKI" or "TKI積み" (TKI setup), Japanese players always mean the TD attack setup, while western players mean the TKI 3 opening.